Field of the Invention
Embodiments of the invention generally relate to a collimator utilized in a physical vapor deposition chamber for forming a metal containing layer on a substrate, and more particularly, a bipolar collimator utilized in a physical vapor deposition chamber for forming a metal containing layer on a substrate in a semiconductor manufacturing process.
Description of the Background Art
Reliably producing submicron and smaller features is one of the key technologies for the next generation of very large scale integration (VLSI) and ultra large scale integration (ULSI) of semiconductor devices. However, as the miniaturization of circuit technology is pressed, the shrinking dimensions of interconnects in VLSI and ULSI technology have placed additional demands on the processing capabilities. The multilevel interconnects that lie at the heart of this technology require precise processing of high aspect ratio features, such as vias and other interconnects. Reliable formation of these interconnects is very important to VLSI and ULSI success and to the continued effort to increase circuit density and quality of individual substrates.
As circuit densities increase for next generation devices, the widths of interconnects, such as vias, trenches, contacts, gate structures and other features, as well as the dielectric materials therebetween, decrease to 45 nm and 32 nm dimensions, whereas the thickness of the dielectric layers remain substantially constant, with the result of increasing the aspect ratios of the features.
Sputtering, also known as physical vapor deposition (PVD), is an important method of forming metallic features in integrated circuits. Sputtering deposits a material layer on a substrate. A source material, such as a target, is bombarded by ions strongly accelerated by an electric field. The bombardment ejects material from the target, and the material then deposits on the substrate.
Physical vapor deposition process has more recently been adapted to deposit material in trenches and vias with high aspect ratios formed on substrates. A dielectric layer is generally formed over a conductive layer or feature and patterned to expose the conductive feature at the bottom of a via or trench. A barrier layer is generally deposited to prevent interdiffusion between layers, and then metal is sputtered into the trench.
In a physical vapor deposition process, fast-moving ions barrel into the target, dislodging particles from the target surface. The particles may be charged by the interaction with the incident ions through a charge transfer mechanism. Alternatively, the particles may be charged through interaction with any electric fields existing in the space, or the particles may remain uncharged. Deposition generally occurs faster on field regions and near the tops of trench sidewalls. During deposition, ejected particles may travel in all directions, rather than travelling in directions generally orthogonal to the substrate surface, thereby resulting in overhanging structures formed on the corners of the trench before penetrating deeply into the trench. Overhang may result in metal plugs with holes or voids formed therein. For example, overhang portions on opposite sides of a trench may grow together, resulting in premature closing and thus preventing complete filling of the trench and forming a hole or a void. Such holes are not conductive, and severely diminish the electrical conductivity of the formed feature. As devices formed on semiconductor substrates grow smaller and smaller, aspect ratio, the ratio of height to width, of trenches and vias formed in substrate layers grows larger. Higher aspect ratio geometries has higher degree of difficulty to fill without voids.
Conventionally, controlling the ion fractions or ion density reaching to the substrate surface at a desired range may improve the bottom and sidewall coverage during the metal layer deposition process. In one example, the particles dislodged from the target may be ionized and accelerated under an electrical bias applied to the substrate so as to encourage particles to travel down into the trench before early closing-up of the trench. It is believed that by controlling the ion fraction/ion density reached onto the substrate surface may efficient promote ion trajectory reaching down to the bottom of the trench. The accelerated ions may travel more uniformly in a direction orthogonal to the surface of the substrate. As accelerated ions approach the substrate surface, momentum carried from the accelerated ions may reach deep down into the trench, whereupon they deflect toward the trench sidewall under the influence of the electrical bias. Nonetheless, the deeper penetration into the trench reduces the effect of overhang near the top of the sidewall. However, as the aspect ratio of the trenches is getting higher and the substrate size is becoming larger, it has become more difficult to control the ion fraction/ion density reaching down to the trench bottom and also more difficult to uniformly distributions across the substrate surface. Thus, physical vapor deposition process remains a challenge to overcome the increasingly vexing problem of overhang management.
Therefore, there is a need for an improved method and apparatus for forming a metal containing layer with good bottom and sidewall management.